The present invention relates to an air-intake manifold for an internal combustion engine such as an automobile engine and particularly, to sound insulation at air-intake pipes that form an air-intake manifold.
An air-intake manifold for an internal combustion engine includes a plurality of air-intake pipes, which are connected to corresponding cylinders of a multi-cylinder engine and are bundled into groups or a single assembly for preventing the intake air from being interrupted as well as for uniformly distributing the intake air.
FIG. 7 illustrates a typical air-intake manifold for an internal combustion engine to which the present invention is applied. As shown in FIG. 7, an air-intake manifold 1xe2x80x2 comprises a collector 2, an air-intake mount 4, and a plurality of air-intake pipes 3xe2x80x2. The collector 2 and the air-intake pipe mount 4 are connected to each other by the air-Intake pipes 3xe2x80x2. Each of the air-intake pipes 3xe2x80x2 consists of a metal pipe, such as an aluminum pipe, and is bent to have a predetermined shape. Both ends of each air-intake pipe 3xe2x80x2 are fixedly joined to the collector 2 and the air-intake pipe mount 4, respectively.
The conventional air-intake manifold described above involves the following problems. Thus, each air-intake pipe 3xe2x80x2 of the air-intake manifold 1xe2x80x2 receives noise transmission (that may be caused by pulsation of the intake air or mechanical vibrations in the engine) from the air-intake side of the engine, and the noise in turn propagates or dissipates to the outside of the air-intake pipe 3xe2x80x2. For attenuating such propagated or dissipated sounds, a technique has been used to cover the air-intake pipes 3xe2x80x2 with a sound insulating cover that is made of a synthetic resin material or is made of a two-layer steel or aluminum sheet.
However, the sound insulating cover may increase the cost, and in some cases, the appearance of the air-intake pipes 3xe2x80x2 covered with the insulating cover is not favorable for the automobile engine. Alternatively, the air-intake pipes 3xe2x80x2 may be covered entirely with sound insulating materials. However, the cost will be increased also in this case. In addition, the dissipation of heat will be substantially interrupted.
The present invention has been made in view of the above aspects and is aimed to provide an air-intake manifold for an internal combustion engine, in which propagated or dissipated sounds from the air-intake pipes can effectively be attenuated without covering the air-intake pipes with a separate insulating cover or a sound insulating material.
According to the invention of claim 1, an air-intake manifold for an internal combustion engine is provided that comprises a collector, an air-intake pipe mount, and a plurality of air-intake pipes connecting between the collector and the air-intake pipe mount, wherein each air-intake pipe is fabricated by bending a substantially straight double metal with smooth pipe surfaces that includes an outer pipe and an inner pipe having different natural frequencies from each having a clearance equal to or less than 0.2 mm therebetween, such that the outer pipe and the inner pipe locally slidably contact with each other at an intermediate region, and the outer pipe and the inner pipe are joined at both ends to each other by brazing.
According to the invention of claim 1, while the outer pipe and the inner pipe of the air-intake pipe locally slidably contact with each other at the intermediate region, an air layer having a thickness equal to or less than about 0.2 mm is formed between the outer pipe and the inner pipe at portions except for the intermediate region.
Therefore, in addition to the sound insulation effect that may be attained by the air layer, the noise attenuation effect can be attained by the relative sliding movement between the outer pipe and the inner pipe at their contact point. Thus, because the outer pipe and the inner pipe have different natural frequencies from each other, the relative sliding movement between them at the contact point may attenuate the vibrations. As a result, propagated or dissipated noises derived from the air-intake pipes can significantly be attenuated in comparison with a conventional single pipe structure that has a wall thickness equal to a sum of the two, outer and inner, pipes.
According to this invention, propagated or dissipated sounds from the air-intake pipes can effectively be attenuated without the use of a separate cover or a sound insulating material. This allows the internal combustion engine to be enhanced in the quietness and to be advantageous in the respect of cost, appearance, and heat dissipation over the conventional one using a separate cover or a sound insulating material to shield the air-intake pipes.
In addition, because the outer pipe and the inner pipe of the air-intake pipe are joined at both ends to each other by brazing, the outer pipe and the inner pipe can share a possible stress that may be generally concentrated on the ends of the air-intake pipe, so that the strength of the air-intake pipe can be considerably improved.
According to the invention of claim 2, in invention of claim 1, the outer pipe and the inner pipe of the air-intake pipe are joined at both ends to each other by brazing.
With the invention of claim 2, the outer pipe and the inner pipe of claim 1 can share a possible stress that may be generally concentrated on the ends of the air-intake pipe, so that the strength of the air-intake pipe can be improved.